Electronic delay detonator

ABSTRACT

Patent of invention of an electronic delay detonator refers to a detonator meant to initiate explosive charges after an electronically predetermined delay time, transforming thermal energy generated by a heat source (2) into electrical energy through a miniaturized thermoelectronical battery (3), packed inside the detonator shell, placing the referred heating source over the heating face (3-A) of the battery (3) which has its opposing face unheated (3-B), being coupled in the detonator a nonelectrical initiation signal conductor medium (1) for the cap, having in the detonator shell the corresponding stages of a capacitor (4) for storage of electrical energy, an electronic timing circuit (5) which provokes the energization of the electric squib, following the detonation of a primary explosive (7) and a consequent detonation of the secondary explosive (8).

BACKGROUND OF THE INVENTION

The present invention refers to an electronic delay detonator, protectedagainst electromagnetic oscillations, intrinsically safe and with a timedelay precision which would be impossible to be obtained throughpyrotechnical charges.

As it is well known by explosive technicians, the delay detonators arecommonly used to connect and start explosive charges in rock blasting,mining, tunnel openings, implosions, or controlled blastings.

Fundamentally, the delay detonators must present a predetermined timedelay between initiation and consequent detonation of the connectedexplosive charge. The delay time is introduced to cause a seriesdetonation of the explosive charges, in order to minimize the vibrationcaused by the blasting, besides propitiating an optimized utilization ofenergy generated by the explosive, achieving the desired efficiency.

Presently, the most used delay detonators make use, for obtaining delaytime, of pyrotechnical columns with varied lengths, containing in itsinterior a mixture of solids capable of burning at a defined velocity.

In spite of many improvements performed along the years, in search ofprecise delay compositions, we can notice that the obtained precision islimited when compared to the possible precision obtainable throughelectronic circuits, which is the state of art technology in the field.

It is worth mentioning that electric sequence devices are used to supplya precise time delay through electric circuits, noting that theconnections between the sequence device and the individual detonatorsare made with electric wires, which causes potential risks to theoperator, due to stray currents, or electromagnetic induction caused byhigh tension lines, broadcast stations, radio transmitters and others.Besides such inconveniences, the electrical wires of the device must beconnected to the detonators during all operation, what becomes difficultbecause of frequent rupture of wires by fragments of blasted material.

It is convenient to mention that the present technology has introducednonelectric shock wave conducting tubes which eliminate the hazardsassociated with electric detonators, as it is described in Patent # PI8104552.

Also known to the blasters is the use of detonating cords with a core ofhigh explosive, connected to elements or blasting caps withpyrotechnical delays, noting that this technological aspect falls uponthe aggravating circumstance of typical ground level noise of detonatingcords, that contributes to the undesirable vibration level, besidesreverting to the unpreciseness of the delay time.

Finally, we have the most advanced technology in the field thatintroduces electronic circuits in delay detonators.

Concerning the matter, is known the document # PI 8807665, published inJun. 5th, 1990, that deals with a process to initiate an ignition systemwith electronically delayed action for explosive charges, in which ismentioned the possibility of energization of the electronic delay systemthrough the melting of a fusible electrolyte, which does not generateelectrical current when in the solid state, but it does so in the liquidstate. This melting would be obtained by the heat generated by thedetonation of an explosive, although the document #PI 8807665 neitherpresents elucidation concerning the materials that could be used forobtaining said energization, nor gives example of a well succeededexperiment with the utilization of the proposed technique. We come tothe conclusion, therefore, that the subject was claimed based in generaland vast principles. It is also known the document # PI 9202520, thatutilizes a piezoelectrical transductor to transform the pressuregenerated by an explosion in the surroundings into electrical energy,which is used to activate a digital delay circuit. The electronic delaydetonator, the object of the present invention, was secretly idealizedand conceived with the purpose of characterizing a technologicalimprovement in the field of safety and precision concerning time delaysfor detonators. Basically, the proposed detonator combines theintrinsical safety of nonelectrical initiation systems with theprecision offered by electronical delay circuits.

SUMMARY OF THE INVENTION

One of the principles of the present invention consists in thetransformation of the thermal energy generated by a heat source such asthe one produced by a shock tube, by the burning of a pyrotechnicalmixture or by the detonation of an explosive, in electrical energy,through a miniaturized thermoelectrical battery properly disposed inorder to generate a difference in electrical potential when their facesare kept at different temperatures.

Consequently, the electric energy generated by the miniaturizedthermoelectrical battery is used to activate an electronic delay circuitwhich, at the end of the programmed delay time, discharges the remainingenergy into an electrical squib which is electrically activated, withwhich there is the detonation of the main explosive in the detonator.

Reference must be made that the possibility of conversion from thermalenergy (heat) into electrical energy is well known--according to manyauthors in pertinent literature--since 1821 when T. J. Seebeckdiscovered that if two wires of different metals have their ends united,and there is a temperature difference in their junctions, there isgeneration of electrical current through the wires.

This effect, worldwide known as Seebeck effect, has been widely used fortemperature measurements through devices called thermocouples. Thetypical thermocouples supply potential difference in the order of 50 to80 μV/°C. and conversion efficiencies in the order of 1%.

Afterwards, with the institution of semiconductors materials, it becameclear that the potential difference generated by the Seebeck effect isgreater when the above mentioned semiconductors are used.

As typical semiconductors we have silicon, tellurium, germanium,selenium, as well as compounds from these elements.

In the presently available technology for electronic devices in general,there is the "doping" of semiconductors compounds with diminutequantities of other elements such us boron, phosphorus, sodium midiodine, to modify its characteristics of electrical conductivity.

Using these semiconductor materials, it is possible to obtain potentialdifferences in the order of 100 to 1000 μV/° C., and conversionefficiencies in the order of 3 to 13%.

The utilization of semiconductors has allowed the development ofthermoelectrical batteries, devices that convert directly heat intoelectrical energy.

As typical use of these devices we can mention: generation ofelectricity in remote localities through burning of combustiblematerial, and obtention of energy in spaceships that travel beyond thereach of solar radiation through heat generated by the decay of aradioactive isotope. It should be observed that conventionalthermoelectrical batteries, applied for the above mentioned uses and forothers, are great dimension devices, and designed for continuous use.

In the electronic delay detonator, object of the present invention, itis used a thermoelectric battery with peculiar characteristics, withdiminute dimensions, developing small electric charges and it is usedonly once, being destroyed at the moment of detonation of the mainexplosive charge.

The present invention will be better understood with reference to thefollowing drawings and their descriptions:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic view of the electronic delay detonator.

FIG. 2 shows the electrical diagram of the thermoelectrical battery.

FIG. 3 shows a schematic view of the thermoelectrical battery.

FIGS. 4 and 5 show miniaturized thermoelectrical battery.

DETAILED DESCRIPTION OF THE INVENTION

According to FIG. 1, the electronic delay detonator has a nonelectricconductor medium of initiation signal for the cap coupled which can be ashock tube or any other means for nonelectric initiation (1) and that,once initiated, provokes inside the detonator generation of thermalenergy through a source of heat (2), that can be the burning of apyrotechnical mixture, detonation of an explosive or the nonelectricinitiation device itself in order to generate a temperature differencebetween the opposing faces (3-A, 3-B), of a miniaturizedthermoelectrical battery (3), with which there is a generation ofelectrical energy, that can be used directly or stored in a capacitor(4), being then the electrical energy discharged through an electronictiming circuit (5), which, after the programmed delay time, will provokethe energization of a squib (6), occurring the detonation of the primaryexplosive (7), therefore, the detonation of a secondary explosive (8).

In the electronic delay detonator, object of the present invention, itis possible to eliminate the primary explosive (7), since there can bethe direct initiation of the secondary explosive (8) by an electricdischarge or by any other means of initiation.

According to FIG. 2, we can see the electric scheme of the miniaturizedthermoelectrical battery, the electrical scheme being composed of aseries connection of conductors composed of different materials (A,B)this connection being with heating junctions (Q) and junctions formaintenance of room temperature, noting Hint in the heating junctions(Q) is applied a temperature substantially higher than room temperature,

The temperature applied to the heating junctions (Q) is generated by aheat source such as the burning of a pyrotechnical material, thedetonation of an explosive or even the signal of nonelectric initiationover the face (3-A) of the miniaturized thermoelectrical battery (3)that corresponds to the heating junctions (Q). Heat being applied toonly one face of the battery creates a temperature differential betweenthe heated face and the opposing, unheated face of the battery.

Consequently, due to the temperature difference between the heatingjunctions (Q) on the heated face 3-A and the junctions for maintenanceof room a temperature (F) on the heated face 3-B a difference ofelectrical potential between the positive (+) and the negative (-)terminals of the miniaturized thermoelectrical battery (3) is formed.

The thermoelectrical battery can be made of a connection of metals ormetallic alloys, forming thermocouples in series. An example of anadequate thermocouple is the one formed by an chromium-nickel alloy anda copper-nickel alloy.

The thermoelectrical battery can also be made of a serial connection ofcouples of "n" and "p" semiconductor materials according to FIG. 3.

In this option, the functioning of the thermoelectrical battery issimilar to the functioning above mentioned and related to the metallicthermocouples.

As an example, among the semiconductor materials can be used: leadtelluride, silicon-germanium alloys, and silicon

Therefore, according to FIG. 3, we have a schematic representation ofthe miniaturized thermoelectrical batted composed by couples ofsemiconductors of the types "N" and "P" (N,P), observing in FIG. 3 thepositive (+) and negative (-) terminals, and the faces of thethermoelectrical battery (3) corresponding to the heating junctions(3-A) and to the unheated junctions (3-B). Also in FIG. 3 the necessaryelectrical isolation in regions is made evident.

The miniaturized thermoelectrical battery, when composed of couples oftype "n" and "p" semiconductors (N,P), can be obtained by the diffusionof doping elements such as phosphorus and boron over a wafer of siliconor another semiconductor material according to scheme evidenced in FIG.3. The diffusion process is usual in the electronical industry.

The miniaturized thermoelectrical battery can be made according to theexhibited in FIGS. 4 and 5, that show in superior and inferiorperspectives the battery (3) which is composed, in this example, bymechanical connection of types "n" and "p" semiconductor threads (N,P)being said threads alternated and connected by metallic connections (L).

The electronic delay detonator, object of the present invention, is notlimited to the employment of determined materials, nor to the employmentof determined manufacture process, nor determined tension values, norelectrical currents, allowing any combination of adequate materials orprocesses which permit the manufacture of a diminute thermoelectricalbattery that basically performs the direct conversion of heat intoelectricity through the Seebeck effect

Also, it should be mentioned that in the present invention, there can beused as many couples of conductors or semiconductors as it is necessaryfor the desired effect.

It must be emphasized that the ELECTRONIC DELAY DETONATOR from thisinvention does not need an explosive detonation placed over the heatedface of the miniaturized thermoelectrical battery, previous to the delaytime, avoiding the premature rupture of the detonator shell and thepossible interference over the explosive to be initiated

Finally, it should be made clear that the miniaturized thermoelectricalbattery (3) presents inherent safety, since it will only achieve theminimum tension for functioning when there is an accentuated differenceof temperature between the heating face (3-A) and the unheated face(3-B) which is impossible to happen without being provoked.

We claim:
 1. An electronic delay detonator comprising:couples forming anonelectric conducting signal medium for the initiation of a blastingcap, a detonator shell comprising corresponding stages of a capacitorfor storage of electrical energy, an electronic timing circuit whichprovokes the energization of an electric squib following detonation of aprimary explosive and a consequent detonation of a secondary explosives,a heat source disposed in an interior of said detonator over a heatedface of a miniaturized thermoelectrical battery, an opposing face ofsaid battery is not heated.
 2. The electronic delay detonator accordingto claim 1 wherein:said battery including a connection of electricalconductors composed of different materials, said connection with heatedjunctions and unheated junctions, respective to said heated face andsaid unheated face.
 3. The electronic delay detonator according to claim1 wherein:said battery being formed by the serial connection of "N" and"P" semiconductor material couples with electrical isolation andmetallic connections between said couples.
 4. The electronic delaydetonator according to claim 1 wherein:battery directly converting heatinto electricity by a Seebeck effect.